Optical fiber connectors are an essential part of practically all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of an optical fiber connector is to optically couple a fiber with the mating device (e.g., another fiber, an active device or a passive device) by holding the end of the fiber such that the core of the fiber is axially aligned with the optical pathway of the mating device.
To effect optical coupling and minimize Fresnel loss, the end of the fiber is commonly presented for mating in a polished ferrule. A polished ferrule assembly is most readily prepared in a controlled setting wherein precision equipment and skilled personnel are available for cleaving the fiber, and terminating it in a ferrule, and polishing the ferrule and fiber to exacting tolerances. However, there is a need for a connector that can be installed in the field where such facilities and personnel are not available. Under these conditions, it is desirable to omit the step of the polishing the ferrule/fiber in the field by instead terminating the fiber in a connector which has a fiber stub already terminated and polished in a ferrule. The terminating fiber is optically coupled to the fiber stub in the connector, often with the use of a refractive index matched gel to improve optical coupling therebetween. The terminating fiber is held in intimate contact with the fiber stub by virtue of a clamping mechanism, which applies a radial force to the terminating fiber to secure it to the connector. Advantageously, this clamping mechanism facilitates straightforward field assembly by obviating the need to handle epoxy and for curing ovens during field termination. Field-installable connectors which have a clamping mechanism are referred to herein as “crimp-type” connectors.
A well-known crimp-type connector is the LightCrimp® connector available through Tyco Electronics (Harrisburg, Pa.) and disclosed in Pat. No. 6,022,150 ('150 patent), which is incorporated herein by reference. Referring to FIG. 10, a longitudinal cross-sectional view of an SC-style connector 100 of the '150 patent is shown. Prior to clamping, this connector receives a terminating fiber in a fiber-receiving passage 118 defined by two clamping members 154, 155. The two clamping members 154, 155 form a clamping insert 112. During actuation, opposing forces are placed on a collar 121 of an axial displacement member 114 and an enlarged collar 139 of ferrule body 103 as shown by force vectors. The opposing forces cause a reaction face 131 of the axial displacement member 114 to engage an end of a sleeve 113. The opposing forces cause the sleeve 113 to telescopically receive the clamping insert 112 and, in so doing, an inner profile of the sleeve 113 engages an outer profile of the clamping insert 112. Cooperating tapers of the inner profile of the sleeve 113 and the outer profile of the clamping insert 112 urge a reduction in the size of the outer profile of the clamping insert 112. The force imposed is sufficient to overcome the mechanical strength of standoffs, which serve to separate the clamping members initially to receive a terminating fiber, and to move the first and second clamping members together to generate a corresponding constriction of a fiber-receiving passage 118 of the clamping insert 112. As the fiber-receiving passage 118 of the first and second clamping members 154, 155 constricts, it places opposing radial forces on the terminating fiber disposed within the fiber-receiving passage 118, thereby securing the terminating fiber to the connector 100.
Although the connector of the '150 patent was revolutionary in many respects and has enjoyed significant commercial success, the applicants have identified a number of factors which contribute to insertion losses from this connector and other similar crimp-type connectors. These losses, in general, relate to the connectors' reliability in aligning and holding fibers accurately without bending or distortion before and during actuation of the clamping mechanism.
Before actuation, the fiber-receiving passageway 118 in the clamping mechanism tends not to be controlled adequately. That is, when the clamping members 154, 155 are inserted in the connector, often a pre-actuation force is applied to engage them and hold them in place. This pre-actuation force, however, can narrow the fiber-receiving passageway 118 excessively such that insertion of the fiber therein becomes difficult or impossible. This difficulty can lead to excessive fiber bending and/or breakage. Conversely, if the clamping members 154, 155 are not pressed together sufficiently during installation, they are not engaged and the space around the fiber-receiving passage 118 can be excessive causing the fiber to leave the fiber-receiving passageway 118, which can cause fiber bending or damage.
During the actuation process, excessive bending can occur in the fiber between the clamping members 154, 155 and the ferrule 102 since the clamping members are necessarily moving during the actuation process. That is, in the prior-art design, both clamping members are designed to cam inward as the sleeve 113 slides past them during the actuation process. Because both clamping members must be free to move inwardly, they cannot be anchored to the ferrule body 103. The allowed movement of the clamping members relative to the ferrule often twists or bends the portion of fiber between the ferrule 102 and the fiber-receiving passageway 118 in the clamping members 154, 155. This bending increases losses and can even break the fiber.
Furthermore, excessive fiber bending can result from excessive actuation force. An improperly maintained crimping tool may apply an excessive amount of clamping force to effect actuation of the clamping mechanism. This force pushes the sleeve 113 forward excessively causing a great deal of force to be transferred to the cramping members 154, 155 as a result of the camming action between the sleeve and the clamping members. This excessive force has been found to push the clamping members forward, even to the point of extruding the clamping members into the passageway 157. Since the ferrule is fixed and the fiber is fixed to the ferrule and the clamping members, pushing the two components together results in the fiber bending, often to the point of breaking.
The problems described above with respect to fiber alignment before and during actuation are exasperated by the fact that the prior art connector has a number of radial cam surfaces and other curved control surfaces which are exceedingly difficult not only to manufacture, but also to measure to ensure compliance with tolerance limits. In particular, the clamping members and the sleeve comprise radial surfaces which are difficult to machine consistently to ensure reliability. Variations in tolerances tend to accumulate which negatively impact the alignment of the fiber before, during and even after the actuation of the clamping assembly.
Therefore, the applicants have identified a need to improve the alignment of the fiber before, during, and after actuation of the clamping assembly to improve its insertion losses. The present invention fulfills this need among others.